feat: Save a checksum for documents and use it to detect conflicts

Signed-off-by: Benjamin Frueh <[email protected]>

Author: benjaminfrueh

composer/composer/autoload_classmap.php

@@ -62,6 +62,7 @@
     'OCA\\Text\\Migration\\Version030701Date20230207131313' => $baseDir . '/../lib/Migration/Version030701Date20230207131313.php',
     'OCA\\Text\\Migration\\Version030901Date20231114150437' => $baseDir . '/../lib/Migration/Version030901Date20231114150437.php',
     'OCA\\Text\\Migration\\Version040100Date20240611165300' => $baseDir . '/../lib/Migration/Version040100Date20240611165300.php',
+    'OCA\\Text\\Migration\\Version070000Date20250925110024' => $baseDir . '/../lib/Migration/Version070000Date20250925110024.php',
     'OCA\\Text\\Notification\\Notifier' => $baseDir . '/../lib/Notification/Notifier.php',
     'OCA\\Text\\Service\\ApiService' => $baseDir . '/../lib/Service/ApiService.php',
     'OCA\\Text\\Service\\AttachmentService' => $baseDir . '/../lib/Service/AttachmentService.php',

composer/composer/autoload_static.php

@@ -77,6 +77,7 @@ class ComposerStaticInitText
         'OCA\\Text\\Migration\\Version030701Date20230207131313' => __DIR__ . '/..' . '/../lib/Migration/Version030701Date20230207131313.php',
         'OCA\\Text\\Migration\\Version030901Date20231114150437' => __DIR__ . '/..' . '/../lib/Migration/Version030901Date20231114150437.php',
         'OCA\\Text\\Migration\\Version040100Date20240611165300' => __DIR__ . '/..' . '/../lib/Migration/Version040100Date20240611165300.php',
+        'OCA\\Text\\Migration\\Version070000Date20250925110024' => __DIR__ . '/..' . '/../lib/Migration/Version070000Date20250925110024.php',
         'OCA\\Text\\Notification\\Notifier' => __DIR__ . '/..' . '/../lib/Notification/Notifier.php',
         'OCA\\Text\\Service\\ApiService' => __DIR__ . '/..' . '/../lib/Service/ApiService.php',
         'OCA\\Text\\Service\\AttachmentService' => __DIR__ . '/..' . '/../lib/Service/AttachmentService.php',

lib/Db/Document.php

@@ -23,6 +23,8 @@
  * @method setLastSavedVersionEtag(string $etag): void
  * @method getBaseVersionEtag(): string
  * @method setBaseVersionEtag(string $etag): void
+ * @method getChecksum(): ?string
+ * @method setChecksum(?string $checksum): void
  */
 class Document extends Entity implements \JsonSerializable {
 	public $id = null;
@@ -33,13 +35,15 @@ class Document extends Entity implements \JsonSerializable {
 	protected int $lastSavedVersionTime = 0;
 	protected string $lastSavedVersionEtag = '';
 	protected string $baseVersionEtag = '';
+	protected ?string $checksum = null;
 
 	public function __construct() {
 		$this->addType('id', 'integer');
 		$this->addType('currentVersion', 'integer');
 		$this->addType('lastSavedVersion', 'integer');
 		$this->addType('lastSavedVersionTime', 'integer');
 		$this->addType('initialVersion', 'integer');
+		$this->addType('checksum', 'string');
 	}
 
 	public function jsonSerialize(): array {
@@ -48,7 +52,8 @@ public function jsonSerialize(): array {
 			'lastSavedVersion' => $this->lastSavedVersion,
 			'lastSavedVersionTime' => $this->lastSavedVersionTime,
 			'baseVersionEtag' => $this->baseVersionEtag,
-			'initialVersion' => $this->initialVersion
+			'initialVersion' => $this->initialVersion,
+			'checksum' => $this->checksum
 		];
 	}
 }

lib/Migration/Version070000Date20250925110024.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\Text\Migration;
+
+use Closure;
+use OCP\DB\ISchemaWrapper;
+use OCP\DB\Types;
+use OCP\Migration\Attributes\AddColumn;
+use OCP\Migration\Attributes\ColumnType;
+use OCP\Migration\IOutput;
+use OCP\Migration\SimpleMigrationStep;
+
+#[AddColumn(table: 'text_documents', name: 'checksum', type: ColumnType::STRING, description: 'CRC32 checksum of document content')]
+class Version070000Date20250925110024 extends SimpleMigrationStep {
+	public function changeSchema(IOutput $output, Closure $schemaClosure, array $options) {
+		/** @var ISchemaWrapper $schema */
+		$schema = $schemaClosure();
+
+		$table = $schema->getTable('text_documents');
+		if (!$table->hasColumn('checksum')) {
+			$table->addColumn('checksum', Types::STRING, [
+				'notnull' => false,
+				'length' => 8,
+			]);
+			return $schema;
+		}
+
+		return null;
+	}
+}

lib/Service/DocumentService.php

@@ -143,6 +143,7 @@ public function createDocument(File $file): Document {
 		$document->setLastSavedVersionTime($file->getMTime());
 		$document->setLastSavedVersionEtag($file->getEtag());
 		$document->setBaseVersionEtag(uniqid());
+		$document->setChecksum($this->computeCheckSum($file->getContent()));
 		try {
 			/** @var Document $document */
 			$document = $this->documentMapper->insert($document);
@@ -310,25 +311,48 @@ public function getSteps(int $documentId, int $lastVersion): array {
 		return $this->stepMapper->find($documentId, $lastVersion);
 	}
 
+
+
 	/**
 	 * @throws DocumentSaveConflictException
 	 * @throws InvalidPathException
 	 * @throws NotFoundException
 	 */
 	public function assertNoOutsideConflict(Document $document, File $file, bool $force = false, ?string $shareToken = null): void {
 		$documentId = $document->getId();
-		$savedEtag = $file->getEtag();
 		$lastMTime = $document->getLastSavedVersionTime();
+		$lastEtag = $document->getLastSavedVersionEtag();
+
+		if ($lastMTime <= 0 || $force || $this->isReadOnly($file, $shareToken) || $this->cache->get('document-save-lock-' . $documentId)) {
+			return;
+		}
+
+		$fileMtime = $file->getMtime();
+		$fileEtag = $file->getEtag();
+
+		if ($lastEtag === $fileEtag && $lastMTime === $fileMtime) {
+			return;
+		}
+
+		$storedChecksum = $document->getChecksum();
+		$fileContent = $file->getContent();
+		$fileChecksum = $this->computeChecksum($fileContent);
 
-		if ($lastMTime > 0
-			&& $force === false
-			&& !$this->isReadOnly($file, $shareToken)
-			&& $savedEtag !== $document->getLastSavedVersionEtag()
-			&& $lastMTime !== $file->getMtime()
-			&& !$this->cache->get('document-save-lock-' . $documentId)
-		) {
+		if ($storedChecksum !== $fileChecksum) {
 			throw new DocumentSaveConflictException('File changed in the meantime from outside');
 		}
+
+		$document->setLastSavedVersionTime($fileMtime);
+		$document->setLastSavedVersionEtag($fileEtag);
+		$this->documentMapper->update($document);
+	}
+
+	/**
+	 * @param string $content
+	 * @return string
+	 */
+	private function computeCheckSum(string $content): string {
+		return hash('crc32', $content);
 	}
 
 	/**
@@ -414,6 +438,7 @@ public function autosave(Document $document, ?File $file, int $version, ?string
 			$document->setLastSavedVersion($stepsVersion);
 			$document->setLastSavedVersionTime($file->getMTime());
 			$document->setLastSavedVersionEtag($file->getEtag());
+			$document->setChecksum($this->computeCheckSum($autoSaveDocument));
 			$this->documentMapper->update($document);
 		} catch (LockedException $e) {
 			// Ignore lock since it might occur when multiple people save at the same time